This invention relates to a method of using materials that are applied to a disk or card or the like, such as would be used for storing information, such that upon subsequent exposure to an ambient condition said applied material changes from a substantially transparent state to one that is substantially more opaque as a consequence of the creation of light scattering centers, color change, and/or reflectivity change, thereby limiting the ability to read information from said disk, card, or the like after the desired information has been read from the disk for a certain duration of time.
U.S. Pat. No. 5,815,484 describes a limited play optical disk using photochromism, defined as a phenomenon whereby irradiation of a material by light exhibiting desirable wavelengths effects reversible or irreversible changes to the optical absorbance of the material. In particular, irradiation of a coating comprising a photochromic material by light alters the reactive material in the coating so as to change the coating from an optically transparent to an optically opaque state. More specifically, the aforementioned prior art describes the combination of light and oxygen as the stimulus that changes the absorbance characteristics of a photochromic material in response to an interrogating beam of light having a wavelength desirably of about 650 nm. It further describes that when the stimulus is exclusively air, such as from the ambient environment, then the reactive material, which for example comprises a compound selected from a group of dye molecules, changes its state as a result of oxidation from an optically transparent to an optically opaque state that absorbs light of desirable wavelengths used for reading the information from the disk. The active material is described as preferably superimposed over some or all of the plurality of data structures in the optical disk, in the form of a coating on a least a portion of the outer surface of the substrate. U.S. Pat. No. 5,815,484 further specifies that if the material were to be interposed between the substrate and the metallic layer then it would be inherently more difficult to manufacture the optical disk.
Compounds I and II, of U.S. Pat. No. 5,815,484, specifically react upon exposure to 650 nm light at an intensity consistent with the light sources for current DVD players. Moreover, these compounds are photoreactive in the presence of oxygen from ambient air upon exposure to either incandescent or fluorescent light. Accordingly, it is required that compounds I and II, as part of a coating applied to a disk, be stored in inert environment, free of oxygen, prior to exposure to the light from sources such as semi-conductor lasers used for the DVD players. U.S. Pat. No. 5,815,484 also specifies that oxygen reactive materials, for example, the dye compound methylene blue, can be used as the reactive compound that in its reduced form exhibits a pale yellow color, and which re-oxidizes to a dark blue color upon exposure to oxygen in ambient air. This dye and other described dye materials only require exposure to oxygen, and not to the combination of oxygen and light, for the desired change in absorbance characteristics. Accordingly, it is also necessary to store the optical disk containing a coating comprising such dyes in an inert environment free of oxygen prior to use in a CD or DVD player. This requires special packaging to prevent or substantially limit diffusion of oxygen, and perhaps also the use of oxygen adsorbing compounds as part of the packaging. Moreover, once the special packaging is removed and the disk is exposed to ambient conditions, then the coating applied to the disk and which contains the reactive materials must also have been protected against solvents that could subsequently be used to remove or alter said reactive materials, and also protected from use of mechanical methods, such as, for example, polishing or grinding that could be used to remove said coating. The use of such reactive compounds does not contemplate the future use of semi-conductor lasers with shorter wavelengths for more advanced optical disk technologies. Specifically, the dye compounds described would not be appropriate for DVD players incorporating the use of lasers emitting at say 405 nm.
U.S. Pat. No. 5,815,484 claims a method of limiting access to data stored on an optical medium wherein said disk comprises an area containing a plurality of readable data structures and which is coincident with a reactive compound superimposed over at least a portion of said data structures of said area. The reactive compound is to be operated in an ambient environment containing oxygen and the absorbance of light by the material, in response to a combination of exposure to oxygen and to irradiation for some duration of time by light having a wavelength within a selected range, is altered causing a change in optical transmission from said area. A requirement of exposure to both ambient environment and irradiation for some duration of time is particularly disadvantageous. The intensity of semiconductors lasers used in CD and DVD players is not uniform from different manufacturers and thus the duration of time for said irradiation will vary for different players. Moreover, the selected range of wavelengths for said irradiation would be difficult to implement, using the methods contemplated, for a range as broad as between about 780 nm and 405 nm, as would be necessary to prevent defeatability of limited play at shorter wavelengths and provide for useful backwards compatibility.
U.S. Pat. No. 5,815,484 further claims an optical disk adapted for use in an optical readout system such that the disk comprises a film of a reactive compound which is operative to change in response to a stimulus applied to the reactive compound. The film is disposed as an overlayer on a substrate that is in a confronting relationship with a reflecting metallic layer or interposed between said metallic layer and the substrate. Said stimulus is either visible light, infrared light, an ambient environment containing light and oxygen, or air. When the claimed optical disk is adapted specifically for the stimulus being only air, then the reactive compound is operative after a duration of time needed to oxidize and change the absorbance characteristics of the material between a transparent and suitably opaque state that absorbs light of the desired wavelength. An optical disk containing a film comprising said reactive compound that is a chemically reduced form of a dye is further claimed. It is also further claimed that an improved optical disk contains a reactive compound responsive to irradiation by the interrogating beam such that the chemical characteristic of the compound is intentionally changed between transparent and suitably opaque states by exposure to the light, such that the altered reactive compound absorbs light of desired wavelengths. The intensity of semiconductors lasers used in CD and DVD players is not uniform from different manufacturers and thus the required reduction in absorbance of the desired wavelengths will vary for different players. Additionally, the signal to noise requirements for detection of reflected light for reading from DVD and CD media by photo-detectors in said players is not uniform for players from different manufacturers. Moreover, absorbance of the selected range of wavelengths would be difficult to implement, using the methods contemplated, for a range as broad as between about 780 nm and 405 nm, as would be necessary to prevent defeatability of limited play at other wavelengths and provide for useful backwards compatibility U.S. Pat. No. 5,815,484 additionally claims a method for limiting access to data stored on an optical disk having a substrate, a metallic layer encoded with information, and a reactive layer through which the radiation passes prior to being reflected for reading, wherein the reactive layer is exposed to an unspecified environmental stimulus that changes the optical characteristic of said reactive layer from an optically transparent state to an optically opaque state. The claimed method suffers from a serious disadvantage that in practice can substantially compromise and defeat the intended objective. Although the patent specifies the importance of a method for forming an opaque state in the reactive layer that absorbs light of the desired wavelengths, opacity is not defined as being able to withstand defeatability of the desired absorbance state that may otherwise occur due to subsequent exposure of the disk to light containing UV and/or visible wavelengths. Exposure of a disk comprising the reactive material to light, such as readily available and obtained from sunlight, mercury arc lamps, Xenon flash lamps, etc. will generally photobleach the opacity of a reactive layer comprising reactive compounds that are photoactive materials such as defined in U.S. Pat. No. 5,815,484. Photobleaching herein is defined as causing a substantial decrease of said opacity exhibited by the reactive layer. Complete photobleaching of the photoactive material in the reactive layer causes said layer to exhibit a change from said opacity to a state of relative transparency. Specifically, U.S. Pat. No. 5,815,484 contemplates and claims the use of quasi-stable photochromic compounds, such as spiropyrans, and the use of organic dye molecules such as methylene blue and related compounds. U.S. Pat. No. 5,815,484 did not contemplate that the preferably formed state of opacity in the reactive layer comprising said photoactive compounds can be photobleached, especially when said compounds are present in an environment that can alter the oxidized state, and consequently the desired absorbance state at certain wavelengths can be modified to cause the reactive layer to exhibit a relatively undesired transparent state. Similarly, undesirable photobleaching can effect a diminution in the level of absorbance exhibited at the desired wavelengths, as well as a shift in the absorbance spectrum such that absorbance at the desired wavelengths diminishes and is no longer adequate to prevent reading of information from the optical disk at the desired wavelengths emitted by the lasers used for the players.
Organic dyes contemplated by U.S. Pat. No. 5,815,484 are converted from a chemically reduced form or leuko state (non absorbing at the interrogating wavelength) to the desired colored state by oxidation via exposure to oxygen in ambient air to form a suitably opaque state that absorbs light at the desired wavelengths. While this process may be reversible, organic dyes generally can be “photobleached” using UV irradiation, such as readily available from sunlight, mercury arc lamps, Xenon flash lamps, etc., and in certain cases loss of opacity can be effected by simply exposing the reactive layer to elevated temperatures. The photo-stability (stability to bleaching processes) and heat stability of the dye is a fundamental problem with organic dyes not contemplated by U.S. Pat. No. 5,815,484. Consequently, the specified and claimed technology would require stabilizers and/or additional protective layers to obviate the obvious defeatability problems.
Another disadvantage with this technology is that it does not anticipate the roadmap for the migration from long to significantly shorter wavelengths for semi-conductor lasers used, for example, by DVD players for reading of information from the optical disk. The currently used lasers irradiate with wavelengths at about 650 nm, while the roadmap devices currently being tested for product introduction as soon as 2002 will have interrogating wavelengths of only about 405 nm. Additionally, the technology does not contemplate the possibility of an optical disc comprising the specified light absorbing reactive layer as being read by more that one type of player. For example, today DVD players commonly used on personal computers, can read both CD and DVD type optical disk media. This requires the use of more than one wavelength for the interrogating laser employed to read information from the two types of optical disks, and additionally the intensity of the lasers and the signal to noise requirements of the photodetectors are not the same. Accordingly, an optical disk that may be unplayable with one type of device may have acceptable play-back characteristics for a second type of device, and thus the desired goal of limited play would not necessarily be achieved. Moreover, the intensities of lasers differ for CD and DVD players made by different manufacturers, as do the signal to noise requirements of the optical pickups or detectors in these players. Consequently, the degree of retained opacity necessary to prevent reading of information on a disk is not the same for one type of manufactured player versus another, and likely also varies as a function of time of use of a particular player.
Other prior art, see for example U.S. Pat. No. 6,011,772 of SpectraDisc Corp., describes a number of methods to limit optical disc readability. Corrosion of the reflective Al layer (or other metal used to reflect light of the laser from information-encoding features so as to read the information on the disk) by the incorporation or delivery of humidity (water) to form an “electrolyte” at or near the surface of the reflective layer and thus catalyze corrosion is such a method. It is preferred that selective corrosion of the Al layer occur so as to cause sufficient loss in reflectivity of the Al layer to prevent optical reading of the encoded information on the disk. This invention, however does not anticipate the current industrial practice incorporating a protective barrier layer, typically SiOx which aggressively prevents the corrosion of the metallic layer. The SiOx layer is necessary to prevent premature corrosion of the metal layer during manufacturing, especially in the case of Al reflective layers where the outermost 100 angstroms of sputtered or vapor deposited layers is known to be completely oxidized in microseconds even in substantially purified environments, a problem that plagued the industry in the past. U.S. Pat. No. 6,011,772 specifies that the reflective layer of FIG. 16 is indeed protected by a barrier layer to prevent such oxidation and physical damage, whereas U.S. Pat. No. 5,815,484 specifies in FIGS. 3, 5, 6, and 7 the use of a barrier layer located adjacent to the reflective layer.
U.S. Pat. No. 6,011,772 further specifies the use of a barrier layer that would be releasably coupled to the disk and that would prevent both machine-reading of the disk and activation of a reading-inhibit agent (RIA). Consequently, the user of the optical disk would be required to remove said barrier layer so as to allow for reading of the information on the disk. Removal of this barrier layer is specified to activate a reading-inhibit agent that will subsequently alter the disk to inhibit reading of the disk after a certain time of exposure of the disk to ambient environment that contains oxygen and moisture and/or irradiation from the reading laser beam of the optical drive. The requirement for diffusion of oxygen and water vapor from the ambient environment through a permeable layer, at a controlled rate, to the metal layer is disadvantageous. The ambient environment is defined by where a particular player is used and thus does not take into consideration the considerable variability in humidity that generally exists in different seasons and in different parts of a country or the world in any season or even in the day versus the night. Accordingly, the limited play time of such a disk could be highly variable depending, for example, if the disk was even made for use in the same state, such as for the case of Dallas versus Houston, Texas where the relative humidity can differ by at least 55%.
Additionally, U.S. Pat. No. 6,011,772 specifies that the read inhibiting agents (hereinafter “RIA”) can be activated by machine-reading the disk such as by the optical radiation that is incident on the disk during machine-reading or by rotation of the disk during machine-reading. This approach suffers from some of the same deficiencies as described above for U.S. Pat. No. 5,815,484. In another embodiment of the barrier layer U.S. Pat. No. 6,011,772 specifies that said layer is formed instead as a closed package that seals the entire optical disk from contact with the ambient oxygen and moisture. This does not reduce the aforementioned disadvantage of requiring activation by both ambient oxygen and moisture.
In another embodiment U.S. Pat. No. 6,011,772 proposes to inhibit reading of information on the disk by incorporation of agents that scatter the reading beam. The scattering mechanism disclosed employs an organic solvent and a polymer layer. The polymer layer, when exposed to an organic solvent, depending on concentration and exposure time, will experience a loss in transparency. In this case the read-inhibiting agent is stated to be the organic solvent working in concert with a polymer film. While this method may work to prevent readability, and is readily effected using common solvents and polymer materials such as polycarbonate, the practicality of dispensing a volatile organic solvent in an electronic device is limited. Solvent flammability, toxicity, and volatility, solvent caused corrosive effects on microelectronic circuitry found in the player, and solvent caused deleterious structural changes to surfaces of the optical components and/or their mounts in the CD and/or DVD player would severely impact general usability and lifetime of the player. These and other effects resulting from use of organic solvents for purposes of scattering the reading laser beam would substantially complicate the use and adoption of this embodiment of the specified technology for the intended purpose of limiting the duration for reading information from the said disk.
In another embodiment the inventor specifies the use of optical radiation from a second optical source (i.e. high pressure arc lamp, fluorescent lamp, incandescent lamp, laser) to activate the read-inhibiting agent. The radiation source is coupled to the interrogation beam such that the RIA is activated after the reading beam has firstly read the data. While this method may provide a method to activate the RIA, the coupling of such a secondary light source is not currently employed in standard optical disc play devices. The incorporation of such an activation mechanism would limit the disc from a practicality standpoint unless the majority of DVD and/or CD players incorporated the secondary light source. Moreover, activation of the RIA and the subsequent increase in absorbance of the wavelength used for the reading beam would require different amounts of absorbance for different levels of irradiance provided by reading beams in players from different manufacturers. U.S. Pat. No. 6,011,772 also describes a second source that would be sufficiently strong so as to obviate need for a RIA, but in this case, for example, the light source could cause ablation creating scattering centers that would limit access to information on the disk immediately after the information is read. A simpler approach is further described as an alternative wherein the read/interrogation beam could itself be used to activate the RIA. In this embodiment the RIA is contemplated to absorb some of the intensity of the interrogation read beam and then the activated RIA would attenuate the interrogating beam further and may inhibit proper reading of the data during the read lifetime of the disc.